1. Field of the Invention
The present invention relates to a tripod constant-velocity universal joint for use in automobiles, industrial machines, etc.
2. Description of the Related Art
FIGS. 10 and 11 of the accompanying drawings show one known tripod universal joint for transmitting rotational power from a drive shaft to a driven shaft at a constant velocity regardless of the angle (operating angle) between the drive shaft and the driven shaft. As shown in FIGS. 10 and 11, the tripod universal joint includes an outer housing 1 having three track grooves 2 defined in an inner circumferential surface 1a thereof and extending in the axial direction of the outer housing 1. The tripod universal joint also includes a tripod spider 4 inserted in the outer housing 1 and having three leg shafts 5 projecting radially outwardly. Three rollers 7 are rotatably mounted respectively on the leg shafts 5 by needle bearing rollers 6 having round end faces, and are rotatably and slidably held against roller guide surfaces 3 of the track grooves 2. Rotational drive power is transmitted between the tripod spider 4 and the outer housing 1.
FIG. 12 of the accompanying drawings is a fragmentary cross-sectional view of one of the rollers 7 mounted on the leg shafts 5 by the needle bearings 6. As shown in FIG. 12, the roller 7 has two axially spaced flanges 7a projecting radially inwardly from respective axially spaced ends thereof. The needle bearing rollers 6, which are assembled against an inner circumferential surface 7b of the roller 7 by a keystone process, are prevented from becoming dislodged in the axial direction of the leg shaft 5 by the flanges 7a. For details, reference should be made to Japanese Laid-Open Patent Publication No. 10-184717, for example.
Generally, each of the needle bearing rollers 6 has opposite round end faces 6a. Therefore, the height h1 of the flanges 7a, which is required to prevent the needle bearing roller 6 from becoming dislodged, needs to be greater than one half of the diameter Da of the needle bearing roller 6, i.e., the height h1 needs to go beyond an axial central position 8 of the needle bearing roller 6. Therefore, as the diameter Da of the needle bearing roller 6 becomes larger, the height h1 necessarily becomes larger, resulting in a reduction in the rigidity of the flanges 7a. As the height h1 becomes larger, the service life of the cutting tool that is used to machine the flanges 7a is shortened, and greater difficulty is experienced in assembling the needle bearing roller 6 against the inner circumferential surface 7b of the roller 7.
Japanese Laid-Open Patent Publication No. 10-184717 discloses certain views showing flat end faces of needle bearing rollers. However, there is nothing specifically disclosed or suggested with respect to the dimensions and shapes of the ends of such needle bearing rollers.